Have you ever stopped to think about the way focal length affects the aesthetic of an image? Even if you're photographing the same scene, selecting different focal lengths can really reshape the aesthetics of your scene. Zooming in and out on the same subject area greatly changes the way that a subject relates to the background and the perceived distance between the two.
Subject to background compression is a powerful effect of longer focal length lenses. Long lenses have a way of flattening images, while wider lenses exaggerate perspective. Ever wonder why an 85mm lens is such a popular choice for portraits? This lens has a nice "flattening" effect on the face that ensures that the nose and other facial features are not larger than life.
While some people hesitate at the thought of using prime lenses (lenses with a fixed focal length), moving your feet and altering composition is all you need to make a great portrait. For most of my portraits, I prefer lenses of a longer focal length, typically a 50mm or 85mm lens. This is for a number of reasons. The first of these being that it serves to flatten the subject. We can hide or lessen geometric facial differences with big telephoto lens. The flattening effect on body features is complimentary to your subject.
Using a long focal length also affects depth-of-field. As you probably already know, the term depth-of-field refers to distances from the camera that are in focus. Although many people assume that depth-of-field is solely related to the aperture of a lens, focal length has just as much (if not more) of an effect on the depth-of-field. With a longer lens, the depth-of-field is reduced, thus throwing the background more out of focus and isolating the subject.
Often, this is an desired effect for portraits. In choosing a longer focal length, you can isolate the area occupied by the subject and shift the viewer's focus on the subject. Conversely, greater depth of field through use of wider focal lengths helps to include the surrounding scene.
However, there is never one best lens or focal length choice. If you're wanting to show how a subject relates to the background, using lenses of different focal lengths can change the way the background appears in relation to the subject.
To illustrate this, I shot a series of test images on a bridge near my house. Notice in these images how the bridge's appearance changes in relation to the model.
I used a variety of focal lengths in order to illustrate this effect. The first lens was a Tokina 12-24mm f/4 lens. The second was a Nikon 35mm f/1.8. The final lens was Nikon's 80-200mm f/2.8 lens at 100mm and 200mm. The lens tests were all shot at f/2.8 to equalize depth of field effects (with the exception of the Tokina, set at f/4).
(Note that these shots were taken on my Nikon D300 and that there is a focal length modifier because it is a DX-format camera)
Let's take a look at some test images. In each of these shots, I attempted to compose similarly, with the model's body nearly filling the frame top-to-bottom. Notice that while she occupies approximately the same amount of space in the photo, the background is greatly altered. Most noticeably, you'll observe that the relative size of the bridge in the background changes greatly across the focal length spectrum.
This first shot was taken at the widest perspective, 12mm, using my Tokina 12-24mm lens. In this shot, notice that all of our perspectives are exaggerated. The lines on the road lead into the background with the bridge. The bridge can just barely be seen in this photo! The ultra wide perspective also greatly increases the depth of field, as you can see almost everything in focus. With this focal length, we've included the entire scene.
In this shot at 35mm taken with Nikon's 35mm f/1.8 lens. This is a midrange focal length. The bridge is now more within our viewing range, and depth-of-field is somewhat less than our 12mm shot. We are still at a fairly wide focal length, but have somewhat zoomed into the scene and have begun to isolate the subject.
Alright, now we're at a sweet spot for portraits, sitting at 100mm on Nikon's 80-200mm f/2.8 lens. Notice that in this photo there is a definite "flattening" effect for the model. The bridge is appearing much closer to the model and we've diminished the leading lines of the road. We are now also starting to elminate the depth-of-field, and thus isolate our subject further. This is a focal length that I typically will shoot for when shooting either waist-up or headshot portraits.
In this final photo, that same lens is now set to 200mm. The subject to background compression is in full effect and our model appears very close to the bridge in comparison to the 12mm shot. Notice that we now have a very shallow depth-of-field and our model is very isolated in relation to the scene. Although we are showing the same subject matter, the differences in focal length have created two scenes entirely different in appearance.
In this tutorial, I have attempted to show you the different advantages that varying focal lengths offer. The test images illustrate that the focal length of a lens can reshape a scene.
Experimenting with these various focal lengths is a powerful part of the creative process. Focal length choice is a huge part of the composition process of an image. You can use a wide lens to lead into a background or create distance, or choose a longer focal length to compress your subject against the background. A focal length of any choice can be a good one depending on the way you envision the scene.
Please share your opinion of the test images above in the comment. Did you prefer the wide angle shot, the telephoto shot or something in between? Also share your tips for choosing focal length.